glossary

accommodation
– the ability of the crystalline lens inside the eye to
alter the focus of the eye in order to view a near or distant object

acuity
– clearness of eyesight

amacrine
cells, retinal – interneurons
in the retina that are responsible for 70% of input to retinal
ganglion cells

amblyopia
– a reduction in vision even through corrective lenses,
with no detectable organic cause; often called “lazy eye”

astigmatism
– an error of ocular focus in
which a circular object is imaged as an ellipse due to unevenness in
the optical power across the meridians of the eye., causing blurred
vision; may be corrected with contact lenses, eyeglasses or surgery

cycles/degree
– a unit of visual acuity which defines the frequency of
alternating patterns of light and dark that is captured within an
angle of one degree at the eye

dendrites
– the branched projections of a neuron that act to
conduct the electrical stimulation received from other neurons to the
cell body of the neuron from which the dendrites project

diopter
(D) – the unit used to designate the refracting power of
a lens or the eye, equal to the reciprocal of its focal length
(expressed in meters)

emmetropia
– the normal refractive state of the eye, in which, with
accommodation relaxed, parallel rays of light will converge to a
sharp focus on the retina

emmetropization
–a natural process that
operates in the early years of life to produce a greater frequency of
emmetropia by reducing the magnitude and variance of ocular errors of
focus

farsightedness;
hyperopia – a condition of the eye
in which objects are imaged behind the retina. Clear vision can be
achieved in some cases through increased accommodation until the
object becomes conjugate with the retina

fovea
– the very central part of the
retina, used for fine detailed vision

frontal
cortex – cortex covering the front regions of each of
the cerebral hemispheres. Primarily active in processing motor
responses such as eye movements and executive function such as
planning, coordinating, controlling and executing behaviour

fusion
–the process by which
visual stimuli imaged on the two retinas are combined into a single
percept

ganglion
cells – neural cells which project from the inner
surface of the retina to key visual centers in the brain

Gaussian
distribution – also referred to as a normal
distribution. A bell shaped distribution where the peak of the
distribution contains the sample mean and values above and below the
mean decline symmetrically in a manner defined by standard deviation
of the sample.

geniculo–cortical
– connections from the geniculate to the cortical areas

hemispherectomy
– a surgical procedure where one cerebral hemisphere is
removed; generally used in extreme cases to treat a variety of
seizure disorders

horizontal
cell – laterally connecting neurons in the retina

inferior
temporal – area in the temporal lobe of the brain

isotropic
– independent of direction

lateral
geniculate body (LGN) – a thalamic
relay nucleus of the brain

lens,
crystalline –the lens
located within the eye that acts to vary the eye’s focal power

monotonic
– a function which preserves the given order; e.g. where
each value is equal to or greater than the previous one or each value
is less than or equal to the previous one

morphology
– the study of the shape and form of things in general

myelin;
myelination – fatty insulation
around an axon which protects the nerve fibers and improves the speed
of conduction of nerve impulses

neural
circuits; neural networks – connections of thousands of
neurons with extraordinary specificity that is essential for normal
function; a network or circuit of functionally related neurons that
perform a specific physiological function

neuroanatomy
– the anatomical organization of the nervous system

neurophysiology
– study of the nervous system function

nucleus
of the optic tract – nucleus in the pretectal area of the brain

occipital
cortex – the cortex covering the
posterior lobe of the brain; involved with vision; also referred to
as “visual cortex”

oculomotor
– pertaining to the movement of the eye

opacity
– the condition of being opaque, such as corneal or
lenticular opacity

optic
nerve – a bundle of ganglion cell axons which projects
from a single eye to the joining fibres from the fellow eye at the
optic chiasm and synapsing at the lateral geniculate body (LGN) optic
tract – continuation of the optic nerve which runs from
the optic chiasm to the lateral geniculate nucleus (LGN)

optics
– branch of physics that describes the behaviour and
properties of light

optokinetic
nystagmus – physiological nystagmus (a repetitive,
rhythmic involuntary movement of the eyes) induced by attempting to
fixate objects traversing the visual field, as when viewing out the
window of a moving train.

ophthalmologist
– a medical doctor who specializes
in the diagnoses and treatment of eye diseases, surgery of the eyes,
and can prescribe glasses and contact lenses

optometrist
– a primary eye care provider who
prescribes glasses and contact lenses, and diagnoses and treats
certain conditions and diseases of the eye

parietal
cortex – the
cortical area covering the middle lobe of each cerebral hemisphere
between the frontal and occipital lobes; it contains important
sensory centers

parvocellular
– neurons of the optic system that project from the
retinal ganglion cells to the lateral geniculate nucleus; sensitive
to colour and more capable of discriminating fine details than
magnocellular neurons

peripheral
retina – area beyond the central retina

photoreceptors
– nerve cells in the retina that are specialized for
capturing light; subdivided into rods and cones

pretectal
nucleus – group of cells constituting several subnuclei
in the pretectal area receiving input from retinal ganglion cells

pulvinar
– nucleus of the thalamus of the brain

reticular
activating systems – part of the brain believed to be
the center of arousal and motivation

retina
– thin sensory tissue which lines
the back of the eye; contains millions of photoreceptors (rods and
cones) that capture light and convert them into electrical impulses
that are sent the brain by way of the optic nerve

retino-geniculate
pathway – neural connections from the retina to the
geniculate

rods
– receptor cells in the retinas
that are sensitive to light and are primarily responsible for
peripheral and night vision

saccade
– an eye movement where each eye
moves in the same direction in order to quickly and voluntarily shift
gaze from one target to another

sinusoidal
pattern – a pattern that varies in space or in time in a
sinusoidal fashion

smooth
pursuit eye movements – the ability of the eyes to
smoothly follow a moving object; the object’s velocity is
detected and matched by the resulting eye movement

spatiotopic
– spatial organization of the neuronal receptive fields,
such that adjacent neurons have receptive fields that include
slightly different, but overlapping portions of the visual field

stereopsis
– the ability to perceive a three
dimensional depth which requires adequate fusion of the images from
each eye followed by disparity detection

stereo
acuity – the smallest angular subtense of a retinal
disparity that can be seen in depth.

sub-cortex;
subcortical – the portion of the brain immediately below
the cerebral cortex

superior
colliculus – a paired subcortical structure in part of
the brain’s tectal area which
processes visual information

synapse
– the junction between the axon terminals of a neuron
and the receiving cell

temporal
cortex –
the cortex covering the lobe located below the frontal and parietal
lobes; involved in perception and recognition of auditory stimuli and
memory

trichromacy
– the condition of possessing three independent channels
for conveying colour information derived from the three cone types
which possess distinct visual pigments

uniocular
– pertaining to one eye

vergence
– the simultaneous movement of both eyes in opposite
directions to obtain or maintain single binocular vision

vestibular
ocular reflex – a reflex eye movement that stabilizes
images on the retina during head movement by producing an eye
movement in the direction opposite to head movement

visual
acuity –the ability
to distinguish object details and shape; the ability to
resolve two separate objects in terms of their angular subtense at
the eye

visual
cortex – located in the occipital
lobe; involved in detection of simple visual stimuli

visual
evoked potential – an evoked potential caused by sensory
stimulation of a subject’s visual field

visual
pathway –
route of the nerve impulses from the retina along the optic nerve,
and optic nerve radiations to the brain's sensory cortex that is
located at the base of the skull

wavelength
– the distance in a periodic wave where a complete cycle
of modulation has occurred